An optical element such as a wavelength multi/demultiplexing element is used for optical communication and optical interconnection. As a promising technique for large-capacity interconnection, it has been recently investigated to transmit optical signals through a Si photonic wire waveguide whose mode sectional area is several hundred square μm×several hundred square μm to improve processing capacity by wavelength division multiplexing (WDM). A characteristic variation among polarization components ascribable to structural anisotropy of the Si photonic wire waveguide is a serious problem in application when a WDM optical signal is demultiplexed in a light receiving part, since a polarization state in a transmission channel of optical signals is not kept constant generally. A MRR (micro-ring resonator) type optical wavelength filter having a WDM polarization diversity structure aimed for the suppression of an influence ascribable to the structural anisotropy of the Si photonic wire waveguide has been proposed.
However, the above-described conventional MRR-type optical wavelength filter has a problem that its applicable range is very limited. For example, it is not applicable to a wavelength multi/demultiplexer in which delayed interferometers (DMZI: delayed Mach-Zehnder interferometers) excellent in terms of low loss and wide transmission bandwidth are connected in multi stages.
Patent Literature 1: Japanese Laid-Open Patent Publication No. 2009-244326